Summary of Work: Improved understanding of the structure of HIV proteins can be useful in unraveling the function of the proteins and in understanding the mechanisms of the function of these proteins. This structural knowledge can also be useful in designing novel anti-HIV agents. X-Ray crystallography is the most accurate technique for determination of protein structures. Major drawbacks of the technique, however, are that it can be very time consuming and is dependent on the availability of protein crystals. Molecular modeling programs, on the other hand, can provide insights into the protein structure based on, amongst other things, homology with proteins whose structures are known. Although this approach is attractive, the results have often been less reliable than desired because insufficient information about the protein is available or the degree of homology with proteins of known structure is less than needed for the development of an accurate model. Furthermore, many proteins are posttranslationally modified. These modifications can regulate the activity of the protein, alter the tertiary structure of the protein, or alter the interactions of the protein. Thus, it is important to determine these posttranslational modifications. HIV gp120 is highly posttranslationally modified by glycosylation. We have previously identified the types of glycans observed at specific glycosylation sites and have noted that high mannose glycans and complex glycans tend to be segregated on the surface of the molecule. We were not able, however, to determine the extent of silylation of the complex glycans. We are currently investigating the use of a combination of carbohydrate affinity chromatography to concentrate the glycosylated tryptic fragments of gp120 followed by LC/MS/MS analysis to determine the extent of silylation of specific consensus glycosylation sites. We are also currently growing cell cultures that express the chemokine receptor CXCR4. We will undertake extensive structural studies of the isolated CXCR4 as well as using it in our receptor-ligand studies.